Formation of Shallow Junctions during Rapid Thermal Processing from Electron‐Beam Deposited Boron Sources

Abstract

Diffusion via rapid thermal processing (RTP) has been investigated for fabrication of shallow p-type layers doped with boron. We used dopant sources deposited by electron beam evaporation in the form of thin boron layers with or without in situ deposited silicon capping films. The deposition process is compatible with the resist mask due to low temperatures and poor step coverage, which facilitate dopant removal via a lift-off process. Sheet resistance measurements together with secondary ion mass spectroscopy and spreading resistance profiling analyses indicate that doping efficiency is high for both types of sources in the temperature range of 900 to 1050°C for 10 to 30 s. Full dopant activation inthe silicon substrate, except for the surface region, has been recorded for all process conditions. High surface concentrations observed in the processed samples were attributed to a residual boron layer. Oxidation during doping via RTP results in diffusion enhancement and in consumption of the boron source. Results of cross-sectional transmission electron microscopy (TEM) analyses confirm fast oxide growth rates during the diffusion processes in an oxygen ambient. No defects within the doped layers have been found for the process conditions used in the experiments.